The female orgasm is a mystery, and not just in that how-the-hell-can-I-make-my-girlfriend-climax kind of way. Scientists just can’t seem to figure out what it’s there for. The most recent theory — popularized in the 2005 book The Case of the Female Orgasm — was that it was just an accidental evolutionary by-product of the male orgasm. Meaning, the orgasm is important for men (no shit) and women share biology with them, in the same way that men have non-functioning (unless you count orgasm via nipple clamps) nipples. But anyway, a recent study of thousands of twins, and how they do or don’t orgasm, failed to prove this theory.

Two scientists — Brendan Zietsch, a geneticist at the University of Queensland and Pekka Santtila of Finland’s Abo Akedemi University — surveyed 1,803 pairs of opposite-sex twins and 2,287 pairs of same-sex twins. If the female orgasm was just a by-product, the thought went, then opposite-sex twins should have similar orgasmic function. But… they didn’t. (Though same-sex twins did seem to have similar orgasmic tendencies.) The theory hasn’t been shot down completely, the researchers note, because self-reported orgasm data is notoriously unreliable. But still, “hasn’t been shot down completely” isn’t exactly the research breakthrough we were hoping for. Which means it’s back to the drawing board for the men in women in lab coats who are trying to get to the bottom of the female orgasm. Hey, if it’s any consolation, most women we know can more than empathize.